Robust high power (>20 mW) all-fibre DFB lasers with unidirectional and truly single polarisation outputs

Summary form only given. Distributed Feedback (DFB) fibre lasers represent an attractive alternative to their semiconductor counterparts when employed both in optical transmission systems. Their use in sensing applications have also been considered. The lasers are compact devices based on a Bragg grating written into, or close to, the core of an optical waveguide that exhibits gain; the wavelength accuracy and stability associated with fibre Bragg gratings are thus inherent to the laser. Ideally lasers must also operate with single sided output to achieve the maximum slope efficiency, and single polarisation operation is necessary if the devices are operated together with polarisation sensitive components (such as e.g. modulators in telecommunication systems). We recently confirmed their suitability for such an application by demonstrating their use as robust transmitter sources in a 4/spl times/10 Bit/s WDM experiment over 200 km of standard fibre @ 1.55 /spl mu/m. In this paper we describe new design issues of DFB fibre lasers that result in highly directional output and we present a novel fabrication technique for generating robust single polarisation operation with higher polarisation purities than those previously reported.